Multi-layer systems have been utilized to coat automobiles for a number of years, but the early development of these systems necessarily employed organic solvents. As environmental regulations became more stringent, and the cost of organic solvents rose, organic-borne systems became less desirable. The recent research emphasis in the area of multi-layer systems, especially basecoat systems has focused on the development of water-borne systems for multi-layer coatings.
The shift from organic solvents to water for dispersing and applying resins in multi-layer systems solved many of the environmental and cost problems associated with the use of organic solvents. Water-borne systems, however, resulted in other problems.
One solution to these problems has been the development of anionic polyurethane resins as described, for example, in Ser. No. 38,385, 4-15-87. These resins exhibit superior coating characteristics in many basecoat/clearcoat multi-layer systems. However, in certain instances these resins may not be compatible with strong acid catalyzed high-solids melamine-containing clearcoats, because of the tendency to exhibit wrinkling, and loss of DI (Distinctness of Image), especially when light colored pigments (white, light blue, yellow, etc.) are used.
The polyurethane resins of the present invention, however, may be used in the above-described melamine-containing systems without the negative characteristics exhibited by anionic resins. Thus, the combination of non-ionic polyurethane basecoats wihh strong acid catalysed clearcoats allows for a lower composite Volatile Organic Content (VOC) than with anionic polyurethane basecoats.
The resins of the present invention have excellent water dispersibility properties, a surprising result considering the absence of salt-forming groups. It is particularly surprising that these resins maintain their water dispersibility even when formulated as principle resins in base coat compositions. It is also a surprising result, considering the water dispersibility of these resins, that the resins of the present invention coalesce and hold firmly onto a vertical panel.
In a further aspect of the present invention the resins are formulated into grind resins for use in basecoats. Yet, aqueous dispersions of nonionic polyurethanes are known in the literature and have been used to prepare films and coatings. Generally, polymer dispersions are unsuitable for use in milling pigments. It is quite surprising that the aqueous dispersions of the nonionic polyurethanes of the present invention are effective grind resins for a wide variety of pigments.
The present invention is, in part, directed to polyurethane coatings to be used in formulating basecoat compositions of multi-layer coating systems. Thes resins exhibit superior coating characteristics, for example, good metallic effects such as very favorable arrangement, fixation, and flip effect of the metallic pigments in the paint film. When non-metallic pigments are used, the resins of the present invention exhibit a high level of decorative effect.
This invention, therefore, relates to the field of polyurethane coatings for use in automobile basecoat/clearcoat systems. In particular, this invention relates to the discovery that incorporating polyether-containing compounds into the backbone of a polyurethane resin provides basecoat coating compositions for a number of substrates.
These polyurethane coating compositions exhibit coating characteristics superior to those taught by the art and are especially useful as basecoats for automobiles.
It is an object of this invention to provide polyether-containing polyurethane resins that can be incorporated into basecoat formulations as principle resins and/or grind resins. It is an additional object of this invention to provide water-dispersible resins which are water-dispersible without incorporating salt-forming groups into the resins.
It is an additional object of this invention to provide water-dispersible polyurethane resins which exhibit superior coating and cosmetic characteristics.
It is a further object of this invention to provide aqueous polyurethane dispersions having favorable characteristics for formulating grind resins.
It is also an object of this invention to provide a method of producing the resins and basecoat compositions described herein.
It is a further ob3ect of this invention to provide a method for coating a metallic or plastic substrate utilizing the resins and basecoat formulations of the present invention.
These and other objects of the present invention are furthered by incorporating polyether-containing polyurethane resins into basecoat formulations.